Silicon-on-insulator (SOI) is becoming more attractive as a photonic material for photonic integrated circuits (PLC) because of its unique features. In this paper, we modeled and simulated the performance of the SOI phase modulator with various doping configuration based on the plasma dispersion effect. The effect of the free injected carrier in the region of the propagating optical mode have been investigated at the optical wavelength of 1.55µm. The proposed device have been integrated in the SOI rib waveguide with trapezoidal cross section structure and four different doping configurations have been chosen which are the n+p+n+, p+n+p+, n+n+p+ and the p+p+n+. Our results show that the n+n+p+ configuration possessed the best modulation efficiency of 0.026V.cm and gained the smallest absorption loss of 1.1dB at 0.95V applied voltage.